Various types of ultrasonic devices are used for surgical applications, for example, in ophthalmic surgery for removing cataracts and other tissue. These devices employ a hollow work tip to transmit ultrasonic energy which emulsifies tissue which is to be removed by suction through the tip. This method is known as "pharcoemulsification". An incision is made in the eye and the vibratable needle inserted for fracturing a cataract. A suction force is applied through the needle interior withdrawing the fragmented cataract. An infusion sleeve surrounds a portion of the needle and supplies a fluid into the eye which thus assists in flushing and removing the fragmented cataract components. The fluid also serves to cool the vibrating needle so as to prevent heating which can cause tissue damage. In addition, the fluid infusion serves to maintain the eye in an inflated pressurized condition during cataract removal.
One problem that has been encountered with prior art devices is that during cataract surgery, fluid leaks from between the edges of the incision and the exterior surface of the infusion sleeve. Loss of this fluid can cause collapse of certain tissue within the eye which could cause damage.
One type of infusion sleeve that has been used for such surgery is made of silicon. However, this was found unacceptable because, as a soft compressible material, the incision tends to compress the non-rigid silicon sleeve against the vibrating needle which results in relative rubbing movement between the silicon sleeve and the vibrating tip. This generates undesirable heat that can result in burns, and shrinkage of ocular tissues surrounding the compressed silicon sleeve. Further, collapse of the infusion sleeve against the vibrating needle constricts the path of fluid flow into the eye thereby hampering efforts to keep the eye pressurized and inflated.
One method for overcoming this deficiency has been to use infusion sleeves made from rigid non-compressible materials, such as polytetrafluoroethylene (PTFE) or metals. While rigid non-compressible sleeves avoid the collapse problem encountered with the soft sleeves, the typical rigid sleeve does not match the contour of the eye incision and therefore continues to allow for leakage through the edges of the incision.
In U.S. Pat. No. 5,084,009, a rigid infuision sleeve is described which reduces leakage in that the rigid sleeve has a ellipsoidal configuration. In an alternative embodiment, a vibrating needle is surrounded by a rigid circular infusion sleeve which itself is then surrounded by a soft deformable infusion sleeve which is circular in cross section, but which then becomes snug fitted by compression induced by the wound incision to assume approximately the ellipsoidal configuration. Thus, when the silicon sleeve is compressed, it compresses against the inner rigid non-compressible sleeve so as to avoid collapse on the needle.
Utilizing the rigid ellipsoidal configuration sleeve has several disadvantages. In particular, in use, the work tip is frequently inserted and removed several times during the course of a procedure and consequently, the direction of the ellipsoidal configured sleeve is important and must be maintained otherwise, leakage can occur as the needle is manipulated within the incision. For example, if turned 90 degrees this could cause damage to the delicate eye tissue.
Utilizing the second embodiment of the '009 Patent requires an instrument with multiple co-axial components which has an increased diameter, requiring an incision size which is somewhat larger and more difficult for a surgeon to manipulate within the incision.
In U.S. Pat. No. 5,188,589, a textured irrigating sleeve is described which utilizes a circular cross-section and a pebbled or granulated interior surface of a sleeve which, though in contact and contactable with a vibrating needle, does allow some fluid to pass thereby. However, the potential for heating still remains, and also the potential for uneven supply of infusion fluid to the eye. In U.S. Pat. No. 4,808,154, a circular infusion sleeve is described which utilizes at least one internal longitudinally extending rib member to guide a flushing fluid through the cylindrical member and to isolate the interior portions of the cylindrical sleeve from the tip member. In essence, collapse is again allowed between the tip and infusion sleeve, the rib engaging the needle. However, again, this results in heating, requiring a larger diameter sleeve and, with a circular cross section with longitudinal ribs, resists the tendency to assume an ellipsoidal shape when placed in an incision.